Ocean Currents Earth Science

Ocean Currents Currents- water in a stream Surface currents- currents that move on or near the surface & are caused by wind Deep current- move very slowly beneath the surface of the ocean & are caused by density differences in water

Ocean Currents: Surface Currents Driving energy source for surface currents is wind Surface currents extend down to a depth of 100m 3 controlling factors in surface currents Wind belts Earth’s rotational effects Location of the continents

Ocean Currents: Surface Currents Wind belts Most directly affect the surface currents Trade winds & westerlies Trade winds at latitudes north & south of the equator Westerlies are located in the middle latitudes North of the equator the trade winds blow from the northeast (Northern Hemisphere) & are usually warm Southern Hemisphere trade winds blow from the south east In both hemispheres they push water to the west

Wind Belts Northern Hemisphere westerlies blow from the southwest…moves currents eastward across the Atlantic & Pacific Oceans Southern Hemisphere westerlies blow from the northwest…moves currents eastward Produce the largest current on earth…West Wind Drift Travels the entire circumference of the earth and is located in the southern part of all 3 major oceans

Ocean Currents: Surface Currents Coriolis Effect Deflection of the earth’s winds and ocean currents based on the rotation of earth Coriolis effect along with the earth’s winds cause gyres Gyres- huge circle of moving water Northern hemisphere- gyre moves clockwise Southern hemisphere- gyre moves counterclockwise

Ocean Currents: Surface Currents Continents The surface current flows against a landmass and is divided and deflected Equatorial Current Warm currents 2 of them both move in a westward direction

Ocean Currents: Surface Currents North Pacific & Atlantic Currents North Atlantic North Atlantic Equatorial Current Warm current that moves water north along the east coast of North America called the Gulf Stream Gulf Stream widens & slows and becomes the North Atlantic Drift Drift- weak current All of those currents form the North Atlantic Gyre

Ocean Current: Surface Currents North Pacific Similar to the North Atlantic Japan Current is equivalent to the Gulf Stream Flows northward & turns into the North Pacific Drift when it spreads out & slows down as it flows towards North America

Ocean Currents: Surface Currents Currents in the Southern Hemisphere Currents here also flow in gyres but in a counterclockwise direction Southern regions of all three major oceans constant westward winds produce the West Wind Drift West Wind Drift is the largest current in the world Because there is no continents to stop it the West wind drift completely circles Antarctica

Ocean Currents: Surface Currents Currents in the Southern Hemisphere cont… Indian Ocean currents follow 2 patterns Southern part the currents follow a counterclockwise gyre Northern part the currents are governed by monsoons Monsoons change directions with the seasons

Ocean Currents: Deep Currents Cold, dense currents that flow beneath the surface of the ocean Much slower moving than surface currents Produced as cold, dense water of the polar regions sinks & flows beneath warmer ocean water toward the equator Movements are the result of density differences Higher density of polar waters is also a result of an increase in salinity Deep-current layer rises only when winds blow the surface water out of the way

Ocean Currents: Deep Currents Antarctic Bottom Water The densest & coldest ocean water in the world Dense, cold water sinks to the bottom & very slowly move north forming the Antarctic Bottom Water current Moves to north to about 40 degrees & takes several hundred years to make the trip

Ocean Currents: Deep Currents North Atlantic Deep Water South of Greenland the water is exceptionally cold & has high salinity causing it to sink Forms a current that travels south underneath the Gulf Stream Flows southward all the way to the Antarctic & over the Antarctic Bottom Water Deep Atlantic currents also are found near the Mediterranean Sea

Ocean Currents: Deep Currents Turbidity Currents Occur when large masses of sediment that have accumulated along a continental shelf or continental slope suddenly break loose and slide downward Causes the water to become more dense than the surrounding water Believed to cause submarine canyons to deepen

Ocean Waves Wave- periodic up and down movement of water Transfer energy 2 basic parts of a wave: Crest- highest point of a wave Trough- lowest point of a wave Wave characteristics Wave height- vertical distance between a crest & a trough of a wave Wavelength- horizontal distance between 2 crests of a wave Wave period- time it takes for one complete wavelength Wave speed= wavelength/period

Ocean Waves Wave Energy Main source of energy for waves is wind The more energy that is transferred the larger the wave becomes Because of surface area… Large waves tend to become larger because the wind has more area to push on Smaller waves tend to die out because there is a very small surface area for the wind to push on Swell- group of long, rolling waves that are the same size

Ocean Waves Water Movement in A Wave Only the energy of wave moves forward, the water itself moves very little The water particles within the wave move in a circular motion Circle traced by each water particle in a wave has a diameter equal to the height of the wave Energy received by a wave decreases as depth increases because the waves receive their energy from the wind Diameter of the circle traced by each water particle decreases as depth increases

Ocean Waves Wave Size 3 factors that affect wave size: Speed of the wind Length of time the wind blows Fetch of a wave Distance that the wind can blow across open water Long fetch produces very large waves Likely to occur during storms Size of a wave will only increase to a certain height to length ratio before it collapses Whitecaps- occur when high wind speeds blow the crest off of a wave

Ocean Waves: Waves & the Shore Breakers Height of a wave changes as the wave approaches the shore As a wave moves into shallow water, the bottom of the wave is slowed by friction but the top of the wave continues to move at its original speed The top of wave gets farther & farther ahead of the bottom & eventually it topples over & forms a breaker. Height of the wave when it topples over is one to two time the height of the original wave

Ocean Waves: Waves & the Shore Breakers cont… Size & force of breakers are determined: Original wave height Wavelength Steepness of the ocean floor close to shore More steep = rapid increase of wave height = breaker with greater force Pacific Coast Less steep = slower increase of wave height = breaker with less force Atlantic Coast

Ocean Waves: Waves & the Shore Undertows & Rip Currents Undertow- water carried onto a beach is pulled back into deeper water by an irregular current Create problems only along shores with steep drop-offs Rip current- form when water from large breakers returns to the ocean through channels in underwater sand bars that are parallel to the beach Flow perpendicular to shore

Ocean Waves: Waves & the Shore Longshore Currents Form sandbars Forms as waves approach the beach at an angle Flow parallel to the shore

Ocean Waves: Wave & the Shore Tsunamis Most destructive waves in the ocean Energy that forms them comes from seismic sea waves not the wind Usually caused by earthquakes on the ocean floor, but also by volcanic eruptions & underwater landslides Have very long wavelength, wave period is about 15 minutes, and speed of 725 km/hr Entire depth of the water is involved in wave motion Height increase greatly as they approach shore

Tides Tides- daily changes in the level of the ocean surface The gravitational pull of the moon on the earth and its waters is the major cause of tides Low tides are formed halfway between two high tides

Tides: Behavior Tidal movement is due to the rotation of the earth and the pull of the moon. Earth rotates from west to east, so tidal bulges appear to move westward around the earth. Because there are two tidal bulges most locations on the ocean have two high tides & two low tides Tidal range- difference in the level of high tide and low tide at specific locations Can vary widely from place to place

Tides: Behavior During period of new moon & full moon the high tides are the highest and the low tides the lowest This is because the sun, moon, & earth are all aligned These are called spring tides During 1st quarter & 3rd quarter phases the daily tidal range is the smallest This is because the moon & the sun are at right angles to each other in relation to the earth These tides are called neap tides

Tides: Variations Tidal patterns are greatly influenced by the size, shape, depth, & location. Atlantic Coast: tides are semidiurnal, which means twice a day Have a fairly regular tidal range Gulf of Mexico: diurnal, which means once a daily Pacific Coast: follow a mixed pattern & have an irregular tidal range Very high followed by very low, then a lower high tide followed by a higher low tide

Tides: Variations Tidal oscillations- caused by the slow rocking motions of ocean water that occur as the tidal bulges move around the ocean basins Produce the world’s greatest tidal range in the Bay of Fundy (tidal ranges is larger than 15m)

Tides: Tidal Currents Tidal current- occurs as the ocean water rises and falls with the tides, it flows toward & away from the coast. Flood tide- when tidal current flows toward the coast Ebb tide- when tidal current flows away from the coast Slack water- time between flood tide and ebb tide with no tidal currents. Tidal bore- surge of water that rushes upstream where a river meets an ocean

Tide Videos http://youtu.be/kJOvxQElfLc http://youtu.be/5W2sM1Ma7YA